Synthetic polyamides stabilized against the action of light and heat



Unite States atent 3,108,091 SYNTHETIC POLYAMIDES STABILIZED AGAINST THEACTION OF LIGHT AND HEAT Gerhard Illing, Neuieiningen, Pfalz, andHelrnut Stahi, Altdorf, near Nurnberg, Germany, assignors to BadischeAnilin- & Soda-Fabrik Aktiengesellschaft, Lndwigshafen (Rhine), GermanyNo Drawing. Filed Jan. 30, 1961, Ser. No. 85,449 Claims priority,application Germany Feb. 3, 1960 2 Claims. (Cl. 260-4555) This inventionrelates to synthetic polyamides stabilized against the action of lightand heat.

In the processing of polyamides, as for example in injection moldingmachines, screw extruders or hydraulic extruders or during spinning, thesame are often exposed to temperatures of about 200 to 340 C. Duringthese operations, as well as when exposed to the action of light and/ orair, the polyamides become discolored with simultaneous impairment oftheir mechanical properties. Discoloration and impairment of themechanical properties become the more pronounced the higher thetemperatures to which the polyamides are exposed.

It is known that the said disadvantages can partly be overcome by theaddition of stabilizers, such as carboxylic acid hydrazides, stearates,thiodiphenylamine, hexamethylene-bis-salicylamide, hydroquinone,aminophenol, o-hydroxyphenoxyacetic acid, tricresyl phosphite and otherorganic phosphorus compounds, lithium hydride, phosphorous acid,hypophosphorous acid or soluble heavy metal polyphosphate complexes. Theeffect of the known stabilizers is, however, relatively poor, and someof them form colored decomposition or oxidation products. It is alsoknown that polyamides can be processed more satisfactorily if aliphaticcarboxylic acids or phosphoric acids are added thereto, but practicallyno stabilization against the action of light, air and elevatedtemperatures is achieved by such substances.

It is the object of the present invention to provide polyamides whichexhibit considerably improved stability against the action of light, airand heat as compared with polyamides stabilized in known manner.

We have found that polyamides which contain as stabilizers 0.05 to 2% byweight, preferably 0.1 to 0.5% by Weight, of hypophosphoric acid (H P Oand/ or a hypophosphate and 0.001 to 1% by weight, preferably 0.001 to0.1% by weight, based on the Weight of the polyamides, of awater-soluble cerium(III) and/ or titanium(III) salt, exhibitparticularly good thermal stability and fastness to light.Hypophosphates which may be used according to this invention are thoseof monovalent to tetravalent metals, for example of alkali metals, suchas lithium, potassium and sodium, alkaline earth metals, such asmagnesium, calcium and barium, metals of groups IIIA and IIIB of theperiodic system of the elements, such as aluminum and cerium, metals ofgroups IB, IIB, IVA and VIIA, such as copper, zinc, titanium, thoriumand manganese, and metals of group VIII, such as iron, nickel andcobalt. All hypophosphates of metals of the said kinds as well ashypophosphoric acid are suitable for the stabilization of polyamidesaccording to the present invention and do not differ very greatly fromone another in their stabilizing action. The hypophosphates ofpotassium, sodium, magnesium, barium and thorium, as for exampletetrasodium hypophosphate (Na P O -H O), disodium dihydrogenhypophosphate (Na H P O -6H O), barium dihydrogen hypophosphate (BaH P Oand thorium hypophosphate (ThP O however, have proved to be especiallysuitable. Water-soluble salts of trivalent cerium or trivalent titaniumthat are suitable for the purposes of the present invention are those ofwhich at least about 1% aqueous solutions can be prepared. Halides, suchas chlorides, bromides and iodides, as well as sulfonates,

formates and acetates of trivalent cerium and trivalent titanium areespecially suitable, as for example cerium(III) chloride, cerium(lll)acetate, titaniumflll) chloride hexahydrate, titanium(lII) acetatehexahydrate and titanium(III) sulfate hexahydrate. Either kind of thesaid substances, i.e. hypophosphates on the one hand and Water-solublecerium(III) or titanium(lll) salts on the other hand, may be used aloneas stabilizers for polyamides. Surprisingly, however, particularlyeifective stabilization is achieved when substances of the two kinds areused together.

Polyamides which can be stabilized with advantage with a mixture of thesaid substances include polycondensation or polyaddition products ofcaprolactam, caprylic lactam and w-aminoundecanoic acid as well as ofthe salts of adipic acid, suberic acid, sebacic acid and undecanoic acidwith hexamethylenediamine and decamethylenediamine, ofheptadecanedicorboxylic acid and bis-(4-aminocyclohexyl)-methane, oftetramethylene diisocyanate and adipic acid or of aliphatic w-aminoalcohols and dicarboxylic acids each with 4 to 34 carbon atoms betweenthe functional groups.

Such polyamides have, in general, k-values of between about 50 and 120,especially between 65 and 90, and can be prepared in the usual manner,for example by the processes described in US. patent specifications No.2,562,797, No. 2,130,523 and No. 2,252,554 and further developments ofthese processes.

In addition to the stabilizers according to this invention, thepolyamides may also contain the usual brightening agents, such as ceriumdioxide, titanium dioxide, thorium dioxide or yttrium trioxide (Y O inamounts of up to about 2% by weight, with reference to the weight of thepolyamides. The compatibility of the said stabilizers and conventionalbrighteners is good.

The stabilizers according to this invention may be added to thepolyamides during their production by polycondensation or polyadditionor also during the further processing of the same, as for example inscrew extruders, screw-type injection molding machines or kneaders.

Further advantages of the said stabilizers are that they do not formcolored decomposition products in the temperature ranges in which thepolyamides are processed or used, and that they are not separated fromthe polyamides during the evaporation of monomeric initial materialsunder reduced pressure or during the extraction of low molecular weightoligomers by boiling water. It is of particular advantage that the saidstabilizers also have a very marked optical brightening effect on thepolyamides.

Polyamides stabilized according to this invention are suitable for theproduction of shaped materials, such as fabrics, injection moldings,cast constructional parts, sheets, films and coatings, which arecharacterized by special brightness and improved fastness to light andto aging.

The invention will be further illustrated, but is not limited, by thefollowing examples. The parts are by weight, and the k-values referredto Were determined according to H. Fikentscher, Cellulose Chem. 13, p.58 (1932).

EXAMPLE 1 1000 parts of hexamethylenediamine adipate are mixed with 3parts of disodium dihydrogen hypophosphate hexahydrate (Na H P O -6H O),0.01 part of titanium(lII) chloride hexahydrate (TiCl -6I-I O), 0.07part of thorium dioxide and 1000 parts of water. Then polycondensationis effected as usual. The melt is then poured into water, and thepolyhexamethylene adipamide is comminuted and dried in conventionalmanner to a water content of less than 0.1% by weight. Thepolyhexamethylene adipamide thus obtained has the properties listed incolumn 2 of the following table. Column 3 specifies the properties ofpolyhexamethylene adipamide stabilized by adding 3 parts of disodiumdihydrogen hypophosphate hexahydrate and 0.01 part of cerium(III)chloride per 1000 parts of hexamethylenediamine adipate As may be seenfrom the foregoing table, polycaprolactam stabilized according to thepresent invention is characterized by extremely good thermal stability.Polycaprolactam of almost equally good thermal stability is andotherwise following the procedure outlined above. 5 obtained by kneadingthe same amounts of the said sta- By way of comparison, column 4 givesthe properties bilizers into the material in a disk kneader. ofunstabilized polyhexamethylene adipamide, whereas 1 columns 5 and 6 listthe properties of polyhexamethylene EXAMPLE 3 adipamide stabilized byadding only 5 parts of sodium 100 parts of polycaprylic lactam (k-valuein concenphosphite (Na HPO and 3 parts of disodium dihydro- 1O tratedsulfuric acid: 76.4) are thoroughly mixed with 0.2 gen pyrophosphate(NfigHgPzOq), respectively, per 1000 P t Of tetrasodium yp p p -4 2 6),0.7 part parts of hexamethylenediamine adipate and otherwise fol- Of a1% aqueous fl l acetate Solution 1 lowing the procedure outlined above.part of titanium dioxide. The resultant mixture is Table 1POLYHEXAMETHYLENE ADIPAMIDE Stabilized with Stabilized with StabilizedStabilized Properties Nfi2H2P2Ou.6H2O N12 2F20a.0H2O Unstabilized withwith Testing specifications and TiClafiHfl) and CeCla NazHzPzO1 Density.1.14 g./em. DIN 53, 470. k-Value 73 4 In cone. H2304, at C. Meltingrange 260263 C Keller-Bank. Tensile strength 850 kg./em. =100% DIN 53,371. Color White Degree of remission- After storing in the air for 3months at 110 C:

Tensile strength 90 90-05% 60-70% 55-60% 45% Color Yellowish.Blaek-brown Yellowish. Yello\visl1 Degree ofremission. 45-50% -48% 510%35-40% 15-20% Referred to Mg0=100%; measured with electrical remissionphotorneter.

The foregoing table above all shows the supreme thermal stability ofpolyhexamethylene adipamide stabilized according to the presentinvention. Almost equally well stabilized polyhexamethylene adipamide isobtained by kneading the same amounts of the said stabilizers into thematerial in an extruder.

EXAMPLE 2 1000 parts of caprolactam are mixed with 1000 parts of water,3 parts of thorium hypophosphate (ThP O and 0.01 part of titanium(III)chloride hexahydrate. Then polycondensation is effected in the mannerusual for caprolactam. Nitrogen is used to force the polycaprolactaminto hot water, and the low molecular weight constituents contained inthe polyamide are extracted with boiling water in the course of 24hours. The polyamide is then ground and dried in conventional manner toa water content of less than 0.1% by weight. The properties of thestabilized polycaprolactam thus obtained are shown in column 2 of thefollowing table. Column 3 lists the properties of polycaprolactamstabilized in the same manner with 5 parts of disodium dihydrogenhypophosphate hexahydrate and 0.01 part of titanium trichloridehexahydrate per 1000 parts of caprolactam. By way of comparison, column4 gives the properties of unstabilized polycaprolactam.

,- After storing in the air for 6 months at Table 3 StabilizedUnstabilized Properties Density Melting range Tensile strengtlL. ColorDegree of remission Tensile strength Color Degree of remission 810lrg./cm. White Table 2 POLYCAPROLACTANI Stabilized with ThPzOg andProperties TiCl3.6H2O

Unstabilized Testing specifications Density 1.15 g./em. Monomer andoligomer level. 0.32%

1.14 g./em.

DIN 53,479.

In eonc. H2804, at 25 C.

-00 7 Yellowish 45-55% -957 Yellowish 48-56% "Keller-Bank. DIN 53,371.

MgO=%.

Determined by extraction with methanol.

We claim:

1. Synthetic polyarnides containing as stabilizers 0.05 to 2% by Weightof a phosphorous compound selected from the group consisting of thoriumhypophosphate and alkali metal hypophosphate and 0.001 to 1% by Weightof a Water-soluble metal salt selected from the group consisting ofcerium(III) salts and titaniumLII I) salts, said percentages being basedon the weight of the pol-yarnides.

2. Synthetic polyarnides containing as stabilizers 0.1 to 0.5% by Weightof a phosphorus compound selected from the group consisting of thoriumhypophosphate and alkali metal hypophosphate and 0. 00 1 to 0.1% byweight of a Water-soluble metal salt selected from the group consistingof halides, sulfates, formates, and acetates of trivalent cerium andtrivalent titanium, said percentages being based on the Weight of thepolyamides.

References Cited in the file of this patent UNITED STATES PATENTS2,224,695 Prutton Dec. 10, 1940 2,905,555 Fuchsman et a1. Sept. 22, 1959FOREIGN PATENTS 767,897 Great Britain Feb. 6, 1957 OTHER REFERENCESEphraim: Inorganic Chemistry, 5th Ed. by Theme et al., -IntersciencePublishers, N.Y., 1949, pp. 728-30.

1. SYNTHETIC POLYAMIDES CONTAINING AS STABILIZERS 0.05 TO 2% BY WEIGHTOF A PHOSPHOROUS COMPOUND SELECTED FROM THE GROUP CONSISTING OF THORIUMHYPOPHOSPHATE AND ALKALI METAL HYPOPHOSPHATE AND 0.001 TO 1% BY WEIGHTOF A WATER-SOLUBLE METAL SALT SELECTED FROM THE GROUP CONSISTING OFCERIUM (III) SALTS AND TITANIUM (III) SALTS, SAID PERCENTAGES BEINGBASED ON THE WEIGHT OF THE POLYAMIDES.